Heretofore, there has been suggested a hybrid power supply device where a fuel cell, which receives supply of a reactant gas (a fuel gas and an oxidizing gas) to generate a power, is mounted together with a secondary cell such as a storage battery. For example, in recent years, there has been suggested a hybrid power supply device including a main power source part (a fuel cell), an auxiliary power source part (a battery), and a voltage regulating part (a DC-DC converter or the like) which regulates an output voltage of the main power source part to a predetermined direct-current voltage and outputs the regulated direct-current voltage (see Patent Document 1). The voltage regulating part of such a device is configured to operate in one of a feedforward drive mode and a feedback drive mode in accordance with operation parameters of the main power source part.